1. Field of the Invention
The present invention relates to a signal reproducing apparatus for removing cross modulation interference components caused by secondary distortion or tertiary distortion generated during recording and operations in a video disc system, a video tape recorder or the like.
2. Description of the Prior Art
In a video disc system, when reproducing a video FM signal after, cross modulation occurs between a video FM modulation wave fc and an audio FM modulation wave f.sub.1 superposed in the low band. In particular, a cross modulation component caused by secondary distortion fc+f.sub.1 is demodulated as an interference signal of frequency f.sub.1 in the deteriorates video signal, which deteriorated the reproduced picture quality significantly.
Hitherto, various methods have been proposed for removing the cross modulation component f.sub.1. For example, a method disclosed in the Japanese Patent Publication No. 59-29992 reduces the cross modulation interference by subtracting the audio modulation signal from the demodulated video signal.
Alternately, according to the Japanese Laid-open Patent No. 58-203605, the reproduced video FM signal is further phase-modulated to reduce the cross modulation interference.
In these prior art methods, however, there is no practical is disclosure directed to a method of adjusting the subtraction level when eliminating the cross modulation components.
Actually, the cross modulation level differs significantly from one disk to other, and even in a same disk, the cross modulation level varies between the outer circumference and inner of the disk circumference. As such, the cross modulation can not be satisfactorily removed in the conventional methods, and in some instances the cross modulation interference is increased.
Further, in the magnetic recording and reproducing apparatus such as the video tape recorder, a tertiary distortion occurs which is theoretically caused by the electromagnetic conversion characteristic. The same problems described above are encountered in removal of cross modulation interference caused by tertiary distortion.